The present invention relates generally to piezoelectric speakers and more particularly to piezoelectric speakers suitable for use in radiotelephones.
Radiotelephones which are hearing aid compatible conventionally rely on leakage from the magnetic field which drives a conventional speaker to provide hearing aid compatibility. Such compatibility is provided by a coil in the hearing aid which is coupled to the leakage field such that the time varying magnetic field of the leakage field induces a current in the coil. Thus, the hearing aid may be provided with the audio from the speaker without requiring amplification of the background noise, such a road noise, or the like.
Recently, however, radiotelephones have been produced utilizing piezoelectric speakers. Piezoelectric speakers are desirable because of their small size and low power consumption. A piezoelectric speaker utilizes one or more piezoelectric elements to drive the speaker. Piezoelectric elements operate such that the element moves in response to a voltage being applied to the element. However, the piezoelectric speaker does not produce significant magnetic fields. Accordingly, piezoelectric speakers are typically not hearing aid compatible as there is not a suitable time varying magnetic field which may induce a current in the hearing aid coil. Thus, radiotelephones utilizing piezoelectric speakers are typically not hearing aid compatible.
In light of the above discussion, a need exists for improved piezoelectric speakers.
One object of the present invention is to provide a piezoelectric speaker suitable for use in a radiotelephone.
A further object of the present invention is to provide a piezoelectric speaker which is compatible with hearing aids.
These and other objects of the present invention are provided by a piezoelectric speaker which provides a magnetic field to couple to a hearing aid coil. The magnetic field induces a current in the hearing aid coil as it appears as a time varying magnetic field to the coil. The time varying magnetic field is preferably proportional to the movement of a piezoelectric member of the piezoelectric speaker so as to induce a current in the hearing aid coil proportional to this movement. Thus, the piezoelectric speaker may provide hearing aid compatibility.
In a particular embodiment of the present invention, a piezoelectric speaker is provided in which a portion of the piezoelectric speaker moves in response to the application of electrical energy to the piezoelectric speaker. A means is provided for generating a time varying magnetic field responsive to movement of the moving portion of the piezoelectric speaker such that a time varying magnetic field is generated when the moving portion of the piezoelectric speaker moves. The means for generating a time varying magnetic field may be a magnetic element coupled to the moving portion of the piezoelectric speaker so as to move responsive to movement of the moving portion of the piezoelectric speaker. In one embodiment, the moving portion of the piezoelectric speaker is a diaphragm and the magnetic element is a magnetic film applied to the moving portion of the piezoelectric speaker. The magnetic element may be made from a magnetic material such as NdFeB.
In another embodiment of the present invention, the magnetic element is coupled to a maximum displacement location of the moving portion of the piezoelectric speaker. The hearing aid compatible acoustic device may be used as a speaker in a radiotelephone.
In a further aspect of the present invention, a method is provided for a hearing aid compatible piezoelectric speaker including generating a time varying magnetic field responsive to motion of the piezoelectric speaker. In one embodiment of the method aspects of the present invention, the generating step includes connecting a magnetic material to the piezoelectric speaker such that motion of the piezoelectric speaker results in motion of the magnetic material.